The present invention relates to a method and a device for diagnosing the failure of a fuel delivery device in a fuel system, for example, in a motor vehicle. In fuel systems used in internal combustion engines having a high piston displacement, it may be necessary to use a plurality of fuel delivery devices in order to cover the maximum fuel consumption under certain operating states.
German Published Patent Application No. 32 47 915 describes a fuel delivery system for internal combustion engines, in particular in motor vehicles. In the fuel delivery system disclosed in this document, a main delivery pump and an additional delivery pump are used. The amount delivered by the electrically controllable additional delivery pump which influences fuel metering is controlled using a controller as a function of the operating state of the parameters characterizing the internal combustion engine such as, for example, rotational speed, power output, acceleration phases or deceleration phases, exhaust values, or temperature values.
In this configuration of a fuel delivery system, the main delivery pump delivers a constant amount of fuel, while the additional delivery pump covers the amount over this constant amount. The fuel delivery system is used in particular in supercharged internal combustion engines. In the fuel delivery system described in German Published Patent Application No. 32 47 915, both fuel delivery units are mechanically driven.
In today""s applications of fuel systems, internal combustion engines are supplied with fuel, the fuel consumption of the engine increasing considerably in certain operating states. If only one fuel pump is used, its failure is not diagnosed, because with the failure of the fuel the engine stalls automatically. However, if two electric fuel pumps are used, for example, in internal combustion engines having a higher fuel consumption and greater piston displacement, the engine normally continues to operate if one of the electric fuel pumps fails.
However, one electric fuel pump operating alone cannot fully cover the high consumption of the engine. As a result, the fuel/air mixture becomes leaner and combustion failure occurs. The unburned fuel/air mixture may reach the hot catalytic converter, damaging it. For this reason, multiple electric fuel pumps have not been used to date in fuel systems of gasoline engines.
Using the option proposed according to the present invention to monitor the operation of a plurality of fuel/air delivery units integrated in a fuel system, the fuel consumption of large engines can be sufficiently covered, so the their fuel supply, including the supply of any ejectors used, can be ensured even at high system pressures. The safety effect that can be achieved with the present invention can be seen in the fact that a mixture that has become leaner is detected in a timely manner through the timely detection of the failure of a electric fuel delivery pump by the electronic engine control system and countermeasures are taken, for example, by limiting the engine power output.
By triggering engine power output limiting, the operating parameters of the internal combustion engine are modified so that combustion failure cannot occur, making sure that an unburned fuel/air mixture fails to reach the catalytic converter of the exhaust system of the vehicle, damaging it. This ensures continued safe operation of the internal combustion engine, the fuel consumption being covered via the still operational electric fuel pumps, the engine being still operable although under limited conditions regarding the engine power that can be obtained.
Through the engine power limiting triggered due to the failure of the electric fuel delivery unit, damage to the catalytic converter of gasoline engines whose fuel systems contain a plurality of fuel delivery units can now be definitively prevented; furthermore, a record can be entered in an error memory through the diagnostic signal, so that the occurrence of an error is detected at the time of a scheduled or unscheduled reading of this memory and can be immediately corrected.
Current measuring elements such as shunts, Hall elements, or Reed contacts can be integrated into the leads to the fuel delivery units for direct and indirect current measuring. A shunt is understood in the following to be a measuring resistor connected in series.
These devices allow currents or voltage drops to be directly or indirectly measured and compared. Furthermore, comparisons with maximum or minimum values provided by the electronic control system can be made.